feat(settings): empty filename template reverts to recorded original filename (#1071)

Redefine the empty download filename template from a no-op to a bulk
revert: FilenameTemplateUseCase resolves the target from each model's
recorded original_file_name sidecar entry (skipping models without one),
which resolves follow-ups 1 and 2 with a single coherent semantic shared
by the download and bulk-apply paths.

Also replace the browser-native confirm() with a self-managed
confirmation modal (filenameTemplateConfirmModal) that stacks above the
settings modal, since ModalManager would close the settings modal when
opening a registered one.

locales/ja.json

@@ -689,9 +689,9 @@
             "applyButton": "[TODO: Translate] Apply to Library Now",
             "applyHelp": "[TODO: Translate] Renames all existing files of this model type according to the template. Warning: renaming changes the relative path seen by ComfyUI loaders, so existing workflows referencing the old filename may need to be updated. The original filename is preserved in each model's metadata.",
             "confirmApply": "[TODO: Translate] Rename all existing files of this model type according to the filename template? This changes the relative path seen by ComfyUI loaders. The original filename is preserved in each model's metadata.",
-            "emptyTemplateInfo": "[TODO: Translate] No filename template configured for this model type — original filenames are kept, nothing to apply.",
+            "confirmRevert": "[TODO: Translate] Restore the recorded original filenames of all previously renamed files of this model type? This changes the relative path seen by ComfyUI loaders. Files without a recorded original filename are skipped.",
             "validation": {
-                "keepOriginal": "[TODO: Translate] Valid (keep original filename)",
+                "restoreOriginal": "[TODO: Translate] Valid (empty template restores original filenames)",
                 "invalidChars": "[TODO: Translate] Invalid characters detected (a filename cannot contain / \\ < > : \" | ? *)",
                 "invalidPlaceholder": "[TODO: Translate] Invalid placeholder: {placeholder}",
                 "validTemplate": "[TODO: Translate] Valid template"
@@ -1626,6 +1626,11 @@
             "tip": "少しずつ確認したい場合は一括モードに切り替え、必要なモデルを選んで「選択項目の更新を確認」を使ってください。",
             "action": "すべて確認"
         },
+        "filenameTemplateConfirm": {
+            "titleApply": "[TODO: Translate] Apply filename template to library?",
+            "titleRevert": "[TODO: Translate] Restore original filenames?",
+            "revertButton": "[TODO: Translate] Restore Original Filenames"
+        },
         "bulkAddTags": {
             "title": "複数モデルにタグを追加",
             "description": "タグを追加するモデル：",